Updated production rules:
rule_2: A2 -> A7 12
rule_7: A3 -> 19 10 A6
rule_15: A6 -> 5 7 A5 6 9
rule_17: A7 -> 15 4 A9
rule_25: A9 -> 11 7 A8 6 3
rule_56: A21 -> 6 1